The most economical way to develop new polymeric products is to blend known polymers. This is much less expensive than developing a new polymer from completely new monomers. To develop a new polymer from monomers may involve developing commercially acceptable methods for the monomer synthesis in addition to the polymer synthesis. Toxicological and environmental concerns are also raised when a new monomer is introduced in commerce. Thus, more and more polymer manufacturers are turning to polymer blends for new products. The difficulty with many polymer blends, however, is that most blends of polymers are grossly incompatible; that is, one achieves the worst possible properties from the component polymers because the polymers do not want to finely disperse and adhere to each other. "Technological Compatibilization" as quoted by Norman Gaylord in the article "Use Surfactants to Blend Polymers" in Chemtech, July 1989, page 435 is "the result of a process or technique for improving ultimate properties by making polymers in a blend less incompatible; it is not the application of a technique which induces thermodynamic compatibility, which would cause the polymers to exist in a single molecularly blended homogeneous phase". This means that the polymers do not have to dissolve in each other to be compatible but the domain size of the two polymers is reduced by whatever process or additive is involved. Typically this "technological compatibility" is achieved by the addition of a small amount of a material called a compatibilizer, which causes the polymers to blend more easily. This results in smaller domain size for the discontinuous phase in the polymer blend, and may lead to improved physical properties. Typically, these are block or graft polymers which incorporate polymer segments which are similar to those polymers which the chemist is trying to blend. An example of this is compatibilization of cellulose and polyethylene with a cellulose-ethylene graft copolymer which will compatibilize that pair of polymers. Another way to compatibilize polymers is to prepare the graft polymer in situ by reaction of a polymer with a reactive functional group with another polymer during the mixing cycle. This is illustrated by the figure: ##STR1##
In the figure, the compatibilizer is polymer A containing a reactive functional group X. This group reacts with polymer B to form a graft polymer. This graft polymer acts as a polymeric surfactant to compatibilize polymer A and B.
Polymer blends which take advantage of the best properties of all of the polymers in the blend are very desirable. However, blends which take advantage of the best properties of two or more polymers often cannot be made because the polymers are dissimilar and incompatible. For example, nylon/nitrile rubber blends which exhibit the desirable properties of both the nylon and the nitrile rubber cannot be made by standard blending techniques because nitrile rubber and nylon are very incompatible.